I have a European driving license. Would it be valid in Japan for a car or kart rental?
Japan is listed as a country that requires an IDP (International Drivers Permit) in addition to your domestic driving licence. Source
For kart rental, when I looked into it all required an IDP in addition to a valid foreign driving licence although it does look like not all European countries issue IDPs in the format required.
Belgium, France, Germany, Monaco, Slovenia, Switzerland and Taiwan do not issue permits based on the 1949 Geneva Convention, but instead, have a separate agreement that allows drivers from these countries to drive in Japan for up to one year with an official Japanese translation of their driver's license. A translation can be obtained from the Japan Automobile Federation (JAF) or some of the respective countries' embassies or consulates in Japan.
Found this on one of the Mario Kart rental sites.
CAUTION MariCAR's custom made go-kart is for Streets in Japan. You will need a valid Japanese driver's license, or an International Driving Permit, or an SOFA License for US Forces Japan, or your own driver's license and an official Japanese translation of the license if you are from Switzerland, Germany, France, Taiwan, Belgium, Slovenia, Monaco. Remember! NO LICENSE NO DRIVE!!
So it looks like, if you can get an IDP, you will need one. In the UK they are only £5.50 and can be obtained from most post offices, although I'm not sure where you would get one in other European countries. Your country's national motoring organisation would be the best place to start.